Various types of heart valve prostheses have been developed which operate hemodynamically as a result of the pumping action of the heart. Among the types of heart valves which have been developed are valves having single disc occluders which pivot along an eccentric axes to open and close the heart valves, such as that described in U.S. Pat. No. 3,825,957, and bileaflet heart valves, such as that described in U.S. Pat. No. 4,178,639. Although numerous designs have been proposed for heart valves, the need continues for improved heart valves which are intended for permanent implantation into the human heart.
In its open position, a valve should provide a passageway which is large and which has good flow characteristics so that blood flows freely therethrough with a minimum of drag and eddy currents. A heart valve should be responsive to blood flow to quickly open during the pumping stroke of the heart and snap back quickly when the heart relaxes to prevent regurgitation of the blood. The heart valve must, of course, be biocompatible and thromboresistant, and in this regard, it is important that all surfaces be well washed by blood to prevent stagnation which might lead to eventual clotting. The opening and closing of the valve should be sufficiently soft so as not to cause hemolysis (breaking of blood cells). The heart valve must withstand countless openings and closings, and particular care should be exercised so that the load-bearing surfaces, such as the pivot points and stops, do not wear out during the life of the patient. The above characteristics may be desirably achieved with a simple design which not only simplifies manufacture, but reduces the amount of obstacles to efficient blood flow, reduces the nooks and crannies where blood may stagnate and reduces the quality control problems associated with complexity.
The interengagement structures by which valve members are mounted in heart valve bodies frequently represent the regions where blood is most likely to clot and stagnate. Some designs of heart valves, e.g., U.S. Pat. No. 3,953,898, employ pins or shafts extending from the valve body into the valve member, and such an arrangement can easily lead to blood stagnation and clotting around the mounting members. Other heart valves, such as that described in U.S. Pat. No. 4,123,805, employ more exposed mounting members, yet unless the mounting members are in the direct flow of blood through the heart, the possibility remains that clotting around the mounting members will occur and adversely affect the operation of the heart valve.